Demonstrators marching in support of the early release of Nazanin Zaghari-Ratcliffe in London in November.
Photograph: Peter Nicholls/Reuters

The treatment of Nazanin Zaghari-Ratcliffe, the British-Iranian woman serving a five-year jail sentence in Tehran, amounts to torture, her family have claimed in an appeal to the UN. Richard Ratcliffe, who has resumed campaigning for his wife’s release after promises of an early release or a furlough were unfulfilled, said that a submission had been presented to the UN special rapporteur on torture.

It has outlined why in their view her 22 months of imprisonment over allegations of spying amounted to torture, given “the conditions of solitary confinement, the psychological pressures in the arbitrary detention and court proceedings, and her use as a tool of pressure in wider diplomatic affairs”.

Zaghari-Ratcliffe, who had been accused of running “a BBC Persian online journalism course” and seeking a “soft overthrow” of the Islamic republic, was arrested in April 2016 at a Tehran airport while she and her then 22-month-old daughter, Gabriella, were about to return to the UK after a family visit.

Iranian judicial authorities have touted the idea of an early release, but the exact status of her case is unclear. Last year the authorities moved to put her on a new trial for additional charges, based on claims of fresh evidence that appear to include a BBC pay stub and the contents of her personal email.

She has been told by the deputy prosecutor, her husband said, that her case had left the judiciary and was now in the hand of the Iranian ministry of foreign affairs. Ratcliffe has asked to meet the deputy Iranian foreign minister, who is due to visit London later this month to clarify this claim, which could not be independently verified.

Zaghari-Ratcliffe’s case has become intertwined with Boris Johnson’s political career since the foreign secretary made an erroneous statement last year, which appeared to complicate her legal battle. Johnson has since apologised for mistakenly saying that she was training journalists in Iran, when in fact she was on holiday.

The British woman, who worked as a project manager for the Thomson Reuters Foundation, sounded frustrated about the uncertainty surrounding her case during a recent phone conversation with her husband. Ratcliffe quoted her as saying: “Even when the US embassy was conquered in 1980, [former leader] Khomeini asked to release their women, and kept the men for 444 days. It is now nearly 700 days and you have kept my baby and me away from each other, and away from my husband. How is that acceptable in your religion? You claim to be a Muslim, but that is not the way a Muslim behaves.”

The family believes that Zaghari-Ratcliffe is being punished as a tool of diplomatic pressure. “The level of psychological abuse in Nazanin’s case meets the UN criteria of torture, particularly given her vulnerability as a mother of a young child,” a statement read.

“I think we have passed the threshold where Nazanin’s treatment is torture,” Richard Ratcliffe said. “These ongoing games remain a kind of psychological torture of continual ups and downs, and pressures impacting on Nazanin.”

Ratcliffe said his wife’s wider mood remained volatile in jail, with periods of sadness and anger. Her psychiatrist had increased the strength of her medication, he said, as she continued to complain about “darkly negative feelings, uncontrollable bouts of anger and sometimes feeling numb, unable to join in laughter or conversation”. She has not shown much appetite either, he said.

Some restrictions have also been placed on the conditions of the jail, such as a decrease in phone time and a reduction in food rations due to budget cuts, which has meant no meat or fish, he said.

Gabriella, who is in the care of her mother’s Iranian family, is still able to visit her twice a week.

“At Christmas it felt we were so close to a release. That is what we were told to look out for on 28 December, that is what the computer said. It is what it still says now,” Ratcliffe said. “Talk of temporary release feels far less than the situation merits. Now she is eligible for release. Not just a holiday from prison, but time to come home. But in truth, anything that gets her out of prison this Valentine’s can only be a good thing.

“Three months ago the foreign secretary promised he would leave no stone unturned. It is almost two months since his trip to Iran. It is more than one month since our Christmas hopes did not come to pass. We can’t keep waiting in the doorway of our dreams, waiting for the governments to deliver.”